Age of the Universe: A New Determination

Age of the Universe: A New Determination

Article excerpt

Analyzing the faint glow left over from the Big Bang, scientists report measuring the age of the cosmos with unprecedented accuracy. They claim the age they calculate, 14 billion years, is accurate to within half a billion years.

Astronomers previously had calculated cosmic age by measuring distances to galaxies to deduce the Hubble constant--the current expansion rate of the universe. They then used models to calculate how the rate might have differed in the past. The age obtained this way hovers around 13 billion years. Since measurements of the distances to galaxies are uncertain, however, the Hubble constant isn't known to an accuracy better than 10 percent, and the age of the universe derived using this method is plagued by the same uncertainty.

The new method is based on details of the cosmic microwave background, the radiation that streamed into space when the universe was 300,000 years old. The technique relies on measurements of primordial sound waves that left their imprint on the microwave background. Lloyd Knox and Constantinos Skordis of the University of California, Davis and Nelson Christensen of Carleton College in Northfield, Minn., recently posted their findings on the Internet (http://xxx.lanl.gov/ abs/astroph/0109232).

This age measurement agrees with previous ones and therefore "says that the standard cosmological [model] for the evolution of the universe has all the right elements," notes Wayne Hu of the University of Chicago.

The sound waves are carried by photons generated during the Big Bang, which have since cooled to microwave energies. In the early universe, photons couldn't travel freely but were glued to clumps of ionized matter. That set the stage for producing oscillations. Gravity tended to compress the clumps, but the photons glued to them exerted an outward pressure resisting that compression. After about 300,000 years, the universe cooled sufficiently to set the photons free. …